<nav class="about-nav">
    {yzn:content action="category" catid="$top_parentid" cache="3600" num="6" order="listorder ASC"  return="data"}
    {volist name="data" id="vo"}
    <a {if $catid==$vo['catid']} class="active" {/if} href="{$vo['url']}">{$vo['catname']}</a>
    {/volist}
    {/yzn:content}
</nav>